Antenna



March 18, 1952 R. w. P. KING ANTENNA 2 SHEETS-SHEET 1 Filed June 25,1946 Phase Reversing SlGGVE COAX/AL LINE T0 GEHERHTOK OOAXIAL L NE T0GENERATOR TUHR BLE March 1952 R. w. P. KING 2,589,813

ANTENNA Filed June 25, 1946 2 SHEETS-SHEET 2 TuHQBLE TUNABLE GOAXIALLINE-Tb TWO WIRE TRhuaroRME'k IZwmW:

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y flfoflaeg Patented Mar. 18, 1952 ANTENNA Ronold W. P. King,Winchester, Mass., assignor to United States of America as representedby the Executive Secretary of the Office of Scientific Research andDevelopment Application June 25, 1946, Serial No. 679,076

10 Claims.

This invention relates to antennas. More particularly the inventiondeals with antennas of the type which are employed in the very highfrequency bands and which are suitable for use with metalsurfaced, highspeed aircraft.

As is well known, if electric currents are passed along a. conductor,some electrical energy passes. out into space. When the conductor isextended so that its length is an appreciable part. of a wave length,then the amount of energy radiated as compared with that dissipated asheat may be relatively large and, the radiation. is more efllcient. Atlow frequencies the wave length is very large. while at very highfrequencies the wave, length may be. quite small as represented by theformula where f denotes frequency value and lambda in-. dicates wavelength. At very high frequencies antennas a few inches in lengthrepresenting a quarter wave or half wave are commonly employed with ahalf wave antenna usually being referred to as a dipole.

At speeds of 300 M. P. H, and higher, a. proj ecting member such as anantenna materially dipole radiation will be greatly reduced due to an opositely directed current induced in the rod by thev dipole. However, ifthe ends of the antenna. are connected directly to the rod this is nolonger the case. The. currents in the dipole and rod are then almostexactly in phase. The, re-

suiting device as is known has a large radiation resistance and iscalled a folded dipole. The reason for the reversal of currentis thatthe induced current that would be set up in they rod is exceeded by thein phase current induced directly in the rod by the chargeconcentrations nits-ends- Although this s lut on. t the. difficultynoted. is, suitable for a rod member, it does not afford av means ofpreventing reduction in radiation. in

the case of a relatively large fiat sheet such as is constituted by themetal surface of an airplane in which the antenna is recessed. Theradiation from such a section is extremely small, only out of phasecurrent being present at the surface of the plane.

An object of the invention therefore is to provide an improved antennafor use in airplanes with a view to overcoming the reductioninradiationresulting from proximity of the antenna to a relatively largefiat surface of the plane. Other objects will appear from the followingdescription of the invention.

In this connection, I have discovered that a relatively large conductingsurface need not necessarily reduce greatly the radiation resistance ofa dipole if means is used to excite currents in the conducting surface,which are in phase with the dipole current rather than to excite just.the out of phase image currents. I have further found that I may combinewith a dipole member additional conducting means so arranged thatitfunctions to reverse the phase of currents induced in the flat surface.An important. feature of the invention therefore is the combination witha dipole recessed in a relatively large metal surface of a phasereversing conductor element. which provides for the development andmaintenance of more efficient radiation.

The drawings illustrate preferred embodiments of the invention in whichFigure l is a cross sectional view diagrammatically illustrating theantenna of the invention recessed in an airplane surface.

Figure 2 is a cross sectional view diagrammatically illustrating amodification of the invention;

Figure 3 is a fragmentary plan view illustrating still anothermodification;

Figure 4 isa cross sectional view of an antenna structure similar tothat shown in Fig. 3; and

Figures 5 and 6 indicate alternate arrangements of antenna structuresuch as that shown in Fig. 1.

Considering in greater detail the structures shown in the drawings, Ihave indicated diagrammatically at several points airplane surfaceswhich are, recessed to receive different types of antenna. members ofthe invention. These. antennas are all in general referred to as Bar A ntennas." Each of them. is further classified by reference. to theirstructural detailsor their mode of. activa ion. Thus in. Fig. 1- isillustrated a half bar. antenna; in Fig. 2 is illustrated an enddriven-bar. antenna; in'Figs. 3'and 4 is illustrated a center-driven barantenna; in Fig. is illustrated a crossed bar antenna; and in Fig. 6 isillustrated a parallel bar antenna.

The half bar antenna indicated in Fig. 1 will now be described and thisexplanation, to a large extent, applies to the other antennas shown.Numeral l0 denotes the airplane surface in which is formed a recessedarea I4. A metal bar |2 is located in parallel spaced relation above thearea M. The bar member is of a length h which may for example be Aprotecting cap |6 of a dielectric plastic material may be provided tocover the recessed area and the rod member |2.

At either end of the bar member are secured conductors l8 and 20. Theconductor 20 is connected to the surface l4. The conductor l8 extendsdownwardly through the surface l4 and is slidably received in acylindrical casing IS. The conductor l8 and the casing I9 togetherconstitute a central conductor element of a coaxial line as illustratedat the left-hand side of Fig. 1. Surrounding the conductor l8 and easingI9 is a metal tubing 2| which forms the outside conductorelement of thecoaxial line. The ratio of the diameter of the inner and outerconductors may be so chosen as to provide for suitable attenuationcharacteristics in accordance with the well known properties of coaxiallines.

the rod |2 from the recessed surface may be varied.

In accordance with the invention, 1 further combine with the coaxialline a metal collar 24 having a U-shaped cross section. The collar issecured around the tubing 2| in the manner shown. Supported on thiscollar is another metal tubing or sleeve member 26 which with.the.collar'and the outer surface of 2| constitutes a phase-reversingsleeve assembly. The tubing 26 end is of reduced diameter to allow forsliding contact with the coaxial line and to provide for thephase-reversing sleeve assembly being conductively closed at its bottom.The distance between the conductively closed portion of the collar 24and the airplane surface is preferably The position of the outer sleevemay be varied ifelative to the coaxial line to locate it in a properofiJtuned' position at which maximum beneficial efiects'are secured.

The purpose of the phase-reversing sleeve 26 is to increase theefficiency of radiation by spreading'jthe current on the surface of theplane. Without the sleeve it is pointed out that the surface current isjust the image current of the bar l2. 1 Thiscurrent value falls off veryquickly as one moves'away from beneath the bar. The eff ciencyofradiation .would'also be very small since this current is oppositeindirection to the current in the bar and .hen'ce'tends to cancel its;fieldsso that much larger currents would be r.e-'

qu'ired with correspondingly greater heat loss.

spaced away from the tubing 2| and at its lower It should be observedthat the conductor l8 and the inner surface of the immediatelysurrounding cylindrical tube 2 I act as a open end section of coaxialline as far as current and charge distribution are concerned, 1. e. avoltage maximum occurs at its top.

The sleeve 26 arranged in the manner noted provides a coaxial cavitywhose impedance to a potential difference across its open end is verylarge. This permits large concentrations of charge of opposite sign atthe top of the two tubings. A maximum of current occurs at the bottom ofthis cavity. The large concentrations of charge at the upper rim of theouter tubing function to excite current on the plane surface. l'hecurrents thus induced are in phase with the currents in the bar andtherefore opposite to normal image currents. These in-phase currents inthe plane surface thus serve 'to keep the radiationefficiency relativelyhigh.

It will be seen that with a given bar current, one effect of the sleeveis to reduce or reverse the image currents. The practical effect of thison the behavior of the antenna is to increase both its radiationresistance and its efliciency.

It will also be apparent that an appreciable radiated field can bemaintained by the currents in the sleeve and the plane surface. Thecurrents in the phase-reversing sleeve section build up to quite largevalues, as in a resonant circuit, and these currents together with thesurface currents on the sheet produce a significant radiation field.

The radiation field can in most cases be considdered as due to the barcurrent and its image plus the currents in the sleeves and their images.The relative importance of the phase-reversing sleeves and the bar isdetermined by the ratio of the radius 'y of the sleeve 26 to the heightd of the bar 2 as indicated in Fig. 1. For the extreme condi-' tion ofat being very much less than 7 the phasereversing sleeve and the imagecontribute most of the radiation; the bar and its image in this casemerely acts as a'two-wire line over which energy is fed to thesesleeves. As this relation changes, the bar plays a greater part inproviding radiation. It should also be noted that the phasereversingsleeve if of sizeable diameter is an im-' portant factor in determiningthe distribution of surface current as well as the radiation field.

The end-driven bar antenna structure shown in Fig. 2 is similar to theantenna already described with the difference that two coaxial lines 30and 32 and two phase-reversing sleeve assemblies 34 and 36 respectivelyare employed. One coaxial line is connectedto a generator and the otheras is noted on the drawings is tunable as with a, piston. The sleeveassemblies 34 and 36 are so adjusted as to provide maximum efflciency.In Figs. 3 and. 4 there is indicated one suitable center-driven barantenna arrangement by which phase-reversing sleeves may be employed toadvantage. In this arrangement rod sections 40 and 42 are connected to atwo-conductor line 44. The coaxial cable 46 from the transmitter isconnected to the two-conductor line 44 by a balanced to unbalanced linetransformer section. Two coaxial lines 48 and 50 are connected to thesec-- tions 40 and 42 and are provided with phase-re- Versing sleeves 52and 54. The two side fittings are each connected to an adjustable lengthof adjustable length of coaxial line. The adjustment. in either case isfor the optimum location or the current maximums.

In Fig. 5 I have shown crossed bars 60 and 62 to produce a circularlypolarized field. They are likewise equipped with phase-reversing sleeveassemblies. Similarly, in Fig. 6 there is illustrated a parallel bararrangement with bars 64, 66, 68, and It, each being provided withphase-reversing sleeve assemblies. By varying the arrangement of the barantenna in the manner indicated in Figs. 3, 4, 5 and 6, various otherchanges in the effects produced and the operating characteristics may beobtained.

From the foregoing it will be seen that I have provided an efficient,positive and simple antenna structure which is particularly suited touse with airplanes at high speeds and the difliculties arising out ofrecessed mounting of an antenna in a metal surface are almost entirelyeliminated.

It is intended that the invention may be m0di fled in various respectsin accordance within the limits defined by the claims.

' I claim;

1. An antenna for metal aircraft comprising, an antenna conductorrecessed below the air stream surface of the plane, and substantiallyparallel thereto, a dielectric cover closing the recess, a metal imageplate beneath the antenna conductor and substantially parallel thereto,a coaxial transmission line having its central conductor connected toone end of the antenna and its outer conductor terminating in on openend, and means for impressing reverse phase currents on said imageplate, said reverse phase means including a tubular conductorsurrounding said coaxial line and connected at one end to said imageplate and to the coaxial line at the other end.

2. An antenna for metal aircraft comprising, an antenna conductorrecessed below the air stream surface of the plane and substantiallyparallel thereo, a dielectric cover closing the recess, a metal imageplate beneath the antenna conductor and substantially parallel thereto,a coaxial transmission line having its central conductor connected toone end of the antenna and its outer conductor terminating in an openend, and means for impressing reverse phase currents on said imageplate, said reversing means including a spaced tubular conductorsurrounding the coaxial line one end being connected to the outersurface of the coaxial line at a point substantially a quarter wavelength from said open end, the other end being connected to said metalimage plate, the structure including the outer line conductor, thespaced tubular conductor and the connection therebetween constituting aphase reversing cavity resonator.

3. An antenna for metal aircraft comprising, an antenna conductorrecessed below the air stream surface of the plane and substantiallyparallel thereto, a dielectric cover closing the recess, a metal imageplate beneath the antenna conductor and substantially parallel thereto,a coaxial transmission line having its central conductor connected toone end of the antenna and its outer conductor terminating in an openend, and a connection from the other end of the antenna to the imageplate, and means for impressing reverse phase currents on the imageplate, said phase reversing means including a spaced tubular conductorsurrounding the outer line conductor and forming therewith a tunablecavity resonator, one end of the tubular conductor being connected tothe outer line conductor at a point substantially a quarter wave lengthfrom.

said'open end, the other end being connected to the aforesaid imageplate. i

4. An antenna for a metal aircraft comprisin an antenna conductorrecessed below the air stream surface of the plane and substantiallyparallel thereto, a dielectric cover closing the re. cess and means forincreasing the radiation efficiency of the antenna, said means includinga metal image plate beneath the antenna conductor and means for excitingthe image plate with reverse phase currents, means for direct phaseexcitation of the antenna including a coaxial transmission line havingits inner conductor connected to the antenna and its outer conductorterminating in an open end'substantially inthe plane of said imageplate, said reverse phase exciting means including a quarter wave cavityresonator open toward the antenna and connected between the outer lineconductor and the image plate, said cavity resonator being formed byaspaced tubular conductor surrounding the outer line conductor,

one end being connected thereto at a point. substantially a quarter wavelength from said open end and the other end being connectedto said imageplate.

5. An antenna for an airplane recessedbeneath the air stream surfacecomprising, a coaxial transmission line having its central conductorconnected to the antenna and its outer conduc tor terminating in an openend, and means for increasing the antenna radiation efficiency, saidradiation eificiency means including a metal image plate spaced apartand parallel to the antenna conductor and means for impressing reversephase currents on said image plate, said reverse phase means including aspaced tubular conductor surrounding the coaxial line and cone nectedthereto at a point substantially a quarter wave length from said openend and forming therewith a tunable cavity resonator, and a con.-nection from the other end of said tubular con.- ductor to said imageplate.

6. An antenna for aircraft recessed beneath the air stream surfacecomprising, a metal image plate beneath the antenna, a coaxialtransmis-. sion line for supplying antenna energy having a slidableconnection from the central conductor to one end of the antenna theouter line conductor terminating in an open end, a second coaxial linehaving a central slidable connection to the other end of the antenna theouter line conductor terminating in an open end in line with first openend and an adjustable tuning slug for shorting the central conductor tothe outer conductor, and means for impressing reverse phase currents onthe image plate for increasing the antenna efficiency, said reverse,phase means including a tubular conductor at the end of each linecoaxial with and external thereto, a slidable annular tuning ring foreach line connecting each outer line conductor to its correspondingtubular conductor at points substantially a quarter wave length fromsaid open ends respectively and forming therewith a tunable cavity ineach space between the respective tubular conductors and coaxial lines,and a connection from the ends of the tubular conductors to theaforesaid image surface.

'7. An antenna for aircraft comprising, a center-fed antenna recessedbeneath the air stream surface, a metal image plate beneath the antenna,a coaxial transmission line connected to the center of the antenna, andmeans for impressing reverse phase currents on the image plate forincreasing the antenna efiiciency, said reverse phase means includingtwo tunable coaxial lines each having the central conductor connected toone end of the antenna each outer conductor terminating in an open endat the level of the image plate and a tubular conductor at the end ofeach line concentric with and external thereto, a slidable annulartuning ring for each line connecting the outer line conductor to itscorresponding tubular conductor at a point substantially a quarter wavelength from said open ends respectively and forming therewith a tunablecavity in each space between the respective tubular conductors andcoaxial lines, and a connection from the ends of the aforesaid tubularconductors to the image plate.

8. An antenna system for producing a circularly polarized field foraircraft recessed beneath the air stream surface comprising a pair ofantennas with their electric axes positioned at right angles and inplanes parallel to the surface of the aircraft, a metal image surfacebeneath the antennas, a coaxial transmission line for each antenna forsupplying power having its central conductor connected to one end of oneantenna and its outer conductor terminating in an open end, a secondtransmission for each antenna having its central conductor connected tothe other end of an antenna and its outer conductor terminating in anopen end, means for tuning each second transmission line, and means forimpressing reverse phase currents on the image plate for increasing theantenna efliciency said reverse phase means including a tubularconductor at the end of each aforesaid coaxial line coaxial with andexternal thereto and having a slidable annular tuning ring connectingthe outer line conductor to its corresponding tubular conductor at apoint substantially a quarter wave length from said open end and formingtherewith a tunable cavity for each line in the space between the lineconductor and its ,external tubular conductor, and a connection from theends of each tubular conductor to the image plate.

9. An antenna system for producing a circularly polarized field foraircraft recessed beneath the air stream surface comprising fourantennas arranged in a square with their ends joined together, a metalimage surface beneath the antennas, two coaxial transmission lines forsupplying'power each having its central conductor connected to one ofsaid antenna junctions at opposite vertices of said square and its outerconductor terminating in an open end, two tunable coaxial transmissionlines each having its central conductor connected to one of said antennajunctions at the remaining vertices of the square and its outerconductor terminating in an open end, and means for impressing reversephase currents on the image plate for increasing antenna efficiency,said reverse phase means including a tubular conductor at the end ofeach aforesaid coaxial line concentric with and external thereto andhaving a slidable tuning ring connecting the outer line conductor to itscorrespondin tubular conductor at a point substantially a quarter wavelength from said open end and forming therewith a tunable cavity foreach line in the space between the line conductor and its externaltubular conductor, and a connection from the end of each tubularconductor to the image plate.

10. In an antenna system, an antenna element, a coaxial feed. line atright angles thereto having a central conductor connected to one end ofsaid antenna element and an outer conductor terminated in an open end, ametal image plate spaced apart from and parallel to said antenna, aconnection from the other end of the antenna to said image plate, andmeans for supplying currents to the image plate in reverse phase fromthose normally induced by the antenna, said reverse phase meansincluding a tubular conductor surrounding said line and connectedthereto at a point substantially a quarter wave length from said openend and a connection from the other end of said tubular conductor tosaid image plate.

RONOLD W. P. KING.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS m- A e,

